Hot gas defrosting system



Jan. 23, 1968 1,W, JACOBS Y 3,364,693

HOT GAS DEFROSTING SYSTEM Filed March 28, 1966 INVENTOR.

H25 ATTORNEY ii/ TX 1^@ l United States Patent O 3,364,693 HGT GASDEFROSTING SYSTEM Iames W. `lacohs, Dayton, Ohio, assigner to GeneralMotors Corporation, Detroit, Mich., a corporation of Delaware Filed Mar.28, 1966, Ser. No. 537,781 6 Claims. (Cl. 62-196) ABSTRACT GF THEDISCLOSURE A refrigeration system employing hot gas defrost meanswherein the defrost means is responsive to temperature in the suctionline to initiate and terminate the defrost cycle.

This invention pertains to a simple system for automatically defrostingrefrigerating systems.

Many systems have been devised for automatically defrosting theevaporator of the refrigerating systems. At the present timesubstantially all of the systems used commercially have timing orcounting devices which periodically defrost the evaporator regardless ofthe condition of the frost on the evaporator. Such systems may defrostmore often or less often than needed according to varying conditions.This is usually wasteful.

lt is an object of this invention to provide a very simple, inexpensive,reliable system which will effect the defrosting of the evaporatorefliciently, rapidly and only when needed and for only as long as needed-to complete the defrosting.

lt is another object of this invention to provide a simple, inexpensive,reliable defrosting system which will require only a compact dualthermally operating valve means to effect and terminate the defrostingwithin the evaporator.

These and other objects are attained in the form shown in the drawingsin which a double throw dual alternately operating valve has oneentrance connected to the outlet of the evaporating means and a secondentrance connected to a hot gas bypass circuit. The valve is operated bya snap acting bimetal disc which separates the flow through the twovalves. When the gas flowing out of the evaporating means is warm, thesnap acting bimetal disc will move the valve to close the bypass circuitand keep open the valve at the outlet of the evaporating means so thatthe evaporated refrigerant will flow to the entrance of the motorcompressor unit in the normal manner. When the evaporating means becomesfrosted and the iiuid flowinf7 out of the evaporator consequently ismuch colder, the bimetal disc will snap to the opposite position tosubstantially close the outlet lof the evaporating means and open thehot gas :bypass circuit for ow by passing the condenser to discharge thehot gas into the evaporating means to heat and defrost it. The closedvalve at the outlet of the evaporating means is bypassed by a restrictorin the form of a small hole which makes more efficient the defrosting.When defrosting is completed the fluid flowing through the valve willheat the opposite sides of the bimetal disc sufficiently to return it tothe normal operating condition.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein preferred embodiments of the present invention areclearly shown.

In the drawings:

FIGURE l is a diagrammatic illustration of a reigerating systemembodying one form of my invention;

FIGURE 2 is a sectional view through the defrost valve showing the valvein normal operating condition;

FlGURE 3 is a sectional view through the defrost valve showing the valvein the defrost position.

Referring now to the drawings and more particularly to FIGURE 1, thereis illustrated a sealed motor compressor unit 2i) which may be of thetype illustrated in Patent 3,016,183 issued Jan. 9, 1962. This motorcompressor unit 2t) draws evaporated refrigerant through its inlet 22and lirst discharges the compressed refrigerant through a superheatremoving coil 24 and 4thereafter discharges the compressed refrigerantthrough its outlet 26 into a condenser 28 where the compressedrefrigerant condenses and is collected in the receiver 39 below. Fromthe receiver 36 the liquid refrigerant liows through a ow control devicesuch as a capillary restrictor tube 32 to the evaporator 34 locatedWithin the enclosure 36 containing a medium such as air to be cooled bythe evaporated 34. The evaporating means includes an accumulator 38 atthe outlet of the evaporator.

When the enclosure 36 contains air and moisture vapor and the evaporator34 is operated normally at below freezing temperatures, frost willaccumulate on the evaporator 34 and acts as an insulator to reduce thetransmission of heat from the fluid within the compartment 36 to therefrigerant within the evaporator 34. As the frost accumulates, theefficiency becomes lower so that eventually it is necessary to defrostthe evaporating means. The rate of accumulation of frost depends uponthe amount of moisture within the uid in the enclosure 36. ln ahousehold refrigerator this varies according to the amount of moisturewhich enters the refrigerated compartment when the door is open. Thus,this moisture will vary not only according to the length of time thedoor is opened, but also to the humidity condition of the air in theroom at the various times when the door is opened. These humidityconditions will be influenced by the weather as well as by the amount ofvapor in the room caused by various forms of food preparation.

Since the frost ac-ts as an insulator of the evaporating means andreduces the transmission of heat to the refrigerant owing therein, thefluid owing out of the evaporator means will become colder and have ahigher proportion of liquid content as the frost accumulates. Accordingto my invention, I take advantage of this condition by passing the iiowof refrigerant out of the evaporating means through the Valve casing di)which includes a rs-t entrance conduit 42 extending from the outlet ofthe accumulator 3S into the top of the valve casing 40. This entranceconduit 42 has a valve seat 44 within the casing 46 cooperating with adouble throw valve 46 having an upper face 48 cooperating with the seat44 and having a guide means Sil extending into the entrance conduit 42.The Valve casing 4Q is divided by a snap acting bimetal disc S2 havingits central portion connected and sealed to the valve 46 and its rimheld by and sealed to the casing 4@ betwen the seats 44 and 6l?. Thisbimetal disc 52, when the casing 4t) is at its normal warm temperature,is bowed downwardly as illustrated in FIGURES 2 to keep the Valve face48 separated from the valve seat 44 to provide for dow through theoutlet conduit 54 connecting with the suction conduit 56 leading to thecompressor inlet 22. When the fluid flowing out of the evaporating meansand the accumulator 38 becomes cold, the bimetal disc 52 will snaplupwardly to move the upper face 48 of the valve 46 into contact withthe seat 44 to substantially stop the iiow of refrigerant except for therestricted flow through the aperture 70.

To effect defrosting of the evaporating means 34, 38, there is connectedto the top of the condenser 28 a bypass conduit 58 which extends throughthe bottom of the casing 40 to provide la lower seat 60. The bottom face62 of the valve 46 normally contacts the seat 6h to keep closed thebypass conduit 58. The valve 46 is provided with a downwardly extendingguide 64 extend-ing into the conduit 58. When Ithe bimetal 52 is cooledsufficiently to snap to the upper position shown in FIGURE 3 the Warmgas vfrom vthe -compressor 2) will tlow through the bypass conduit 58through the valve casing 40 to the second conduit portion 66 of thebypass circuit which connects to the bottom of the evaporator 34. Thiswarm gas flowing through the casing 40 will heat the bimetal disc v52 toprepare it for return to .the normal position. The hot gas ows throughthe tubing of the evaporator 34 providing internal heat which eicientlyand rapidly melts the frost from the evaporator 34 and the accumulator3S. This heating is made more eflicient by providing in the tirstentrance conduit 42 a restrictor bypass aperture 70 which bypasses theclosed valve 48 by providing a restricted tlow through it from theoutlet of the accumulator 38 through the valve casing 40 to the outletconduit 54 and the suction conduit 56. This provides a restricted iiowwhich maintains a suiciently high pressure within the evaporating means34, 38 to quickly effect the frosting thereof. The suction conduit 56may have a serpentine heat absorbing portion 57 to evaporate anycondensed refrigerant.

After the frost has melted from the evaporating means, the gas owingthrough the aperture 70 and `ab-ove the bimetal disc `52, in the casing40 will become warmer, thereby supplementing the heating lof the bimetaldisc 52 sufficiently to cause it to snap downwardly from its position inFIGURE 2 to the position shown in FIGURE 3 to restore the system tonormal condition. If desired, the system may be cycled to control thenormal temperature in the enclosure 36 by a thermostatically controlledswitch such as is illustrated and applied to a refrigerating system inPatent 2,351,038 issued Jan. 13, 1944.

While the embodiments of the present invention as herein disclosedconstitute a preferred form, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

1. A refrigerating system including a refrigerant circuit comprising acondenser and a tlow control device and evaporating means and a motorcompressor unit for circulating a refrigerant through said circuit, abypass circuit bypassing said ow control device, closing means fornormally closing said bypass circuit, said evaporating means having anoutlet, and temperature means positioned within the outlet and bypasscircuit and responsive to a predetermined low temperature of therefrigerant flowing out of said outlet for opening said closing meansand said bypass circuit.

2. A refrigerating system as dened in claim 1 in which a normally openclosing means is provided for the outlet of lthe evaporating means, asecond bypass circuit containing a second flow control device forbypassing said normally open closing means, said temperature responsivemeans also having means for closing said normally open closing means,

3. A refrigerating system as defined in claim 1 in which a normallyope-n closing means is provided for the outlet of the evaporating means,a second bypass circuit containing a second flow control device forbypassing said normally open closing means, both of said closing meansbeing in the form of a dual alternately opening and closing valve, saidtemperature responsive means being operatively connected to said valve.

`4. A refrigerating system as dened in claim 1 in which said closingmeans comprises a valve casing containing a dual alternately opening andclosing valve, said casing having a trst entrance connected to theoutlet of said evaporating means and a second entrance connected to saidbypass circuit, said valve cooperating with said entrances toalternately open and close said entrances, said motor compressor unithaving an inlet, said casing having an outlet connected to said inlet,said temperature responsive means being operatively connected to saidvalve.

5. A refrigerating system as delined in claim 1 in which said closingmeans comprises a Valve casing containing a dual alternately opening andclosing valve, said casing having a Ifirst entrance connected to theoutlet of said evaporating means and a second entrance connected to saidbypass circuit, said valve cooperating with said entrances toalternately open and close said entrances, said motor compressor unithaving an inlet, said casing having an outlet connected to said inlet,said temperature responsive means being operatively connected to saidvalve and comprising a snap acting arrangement for controlling theoperation of said valve,

6. A refrigerating system as defined in claim 1 in which said closingmeans comprises a valve casing containing a dual alternately opening andclosing valve, said casing having a tirst entrance connected to theloutlet of said evaporating means and a second entrance connected tosaid byp-ass circuit, said valve cooperating with said entrances toalternately open and close said entrances, said motor compressor unithaving an inlet, said casing having an outlet connected to said inlet,said temperature responsive means being in the form of a snap actingbimetal means located in said casing.

References Cited UNITED STATES PATENTS 2,666,298 l/ 1954 Jones 62-1562,717,494 9/ 1955 Docg 62-278 XR 2,907,181 10/ 1959 Nonomaque 62-196 XR2,944,411 6/1960 McGrath G2-278 XR 3,132,491 5 1964 ISchumacher 62--278MEYER PERLIN, Primary I 'xarrtzrter.y

